From time immemorial, people have tried to prevent theft. They have devised all manner of means to physically stop it including locks, safes, fences, bars, cut-off mechanisms and computer passwords. And they have come up with many systems that identify things as stolen or being stolen. Such "theft identifying systems" can be divided into five types:
1) Permanent Markings
An example is "GOVERNMENT PROPERTY" on a pen signifying that the pen may be stolen if it is outside a government building. The flaw of permanent markings is they can't be changed to reflect a change in the marked item.
2) Seals
Seals reveal whether a thing has been tampered with. They can stop tampering in certain cases but are unsuitable for safeguarding most things.
3) Alarms
Thousands of alarms have been invented not all using sound to inform. The thing that distinguishes alarms is that they require a tripping mechanism to set them off. These mechanisms can often be disarmed and usually add significant costs. Also, alarms are not usually suitable for protecting individual items.
4) Special Inspection Methods
An example is the putting of magnetic strips inside books. If not demagnetized, these strips sound an alarm at special detectors at the exits of bookstores. Another example is the stationing of an inspector at the exit of Baggage Handling in an airport to make sure luggage isn't stolen. Special inspection methods are usually costly and often impractical.
5) Lockable Labels
Certain theft identifying inventions are labels which can be changed but only by the owners of the items the labels are on. These labels might be called "lockable labels" (LLs). A LL is one key element of the system disclosed in the "Description" section below. Theft identifying inventions have cropped up in the past using LL's. For instance, many theft preventing devices using LL's have been patented for preventing the theft of cars. Three examples:
T. McNally, Jr. (U.S. Pat. No. 1,249,798) discloses a sign which is locked over a car's license plate. The sign says, "STOP THIS CAR IF IN MOTION". This sign cannot be removed by a thief without destroying the license plate. M. Downey (U.S. Pat. No. 1,392,869) discloses a sign which is built into the side of a car. The sign can be locked into a position where it says "OWNER OUT". J. Hughes (U.S. Pat. No. 1,636,513) discloses a symbol with two matching elements, one detachable. If the detachable element is missing observers are supposed to realize that the car should be parked. In all these cases, if a thief puts the car in motion, the inventions allow observers to identify the car as being stolen.
These inventions do fall under the system disclosed below. Yet, they are all narrowly designed for motor vehicles (and in one case a bike (E. Andersen, Denmark, U.S. Pat. No. 437,983)) and do not disclose the system disclosed below. Moreover, they can only be changed back and forth between two messages, namely saying whether a car should be in use or not.
Methods related to LL's have been used to safeguard credit cards. Three examples: G. Gibson U.S. Pat. No. 3,583,317) discloses a credit card which can be physically separated into two parts. If both parts are not present, the credit card cannot be used. N. and L. Butterworth (U.S. Pat. No. 4,879,455) disclose a credit card which has digit keys on it and an electrical circuit inside connected to two Light Emitting Diodes (LEDs) which indicate whether the card should be accepted or rejected. Only when the proper Personal Identification Number (PIN) is entered will the green LED indicate "ACCEPT". In these kinds of systems, a thief cannot use a stolen credit card in a store because he or she cannot verify ownership.
Such methods are related to LL's because of the peculiar nature of credit cards. Credit cards are nontransferable and are only supposed to "work" when the owner's identify has been verified. The patented methods physically stop a thief from verifying identity. Hence these methods can be considered physical deterrence much like the yanking of the distributor cap from a car engine is physical deterrence. They can also be considered LL's because when the owner's identity has not been verified, the credit cards carry an implicit or explicit message, "DON'T ACCEPT." The owner can change this message by verifying his identity whereas a thief cannot. However, the methods above for protecting credit cards clearly are not suitable for protecting a wide variety of items.
H. Bochmann (U.S. Pat. No. 4,743,894) discloses a circuit which aids in the recovery of stolen car radios and certain other electronic equipment. The invention allows the owner to enter owner identification information into a radio's memory. This information can only be entered or changed after the proper PIN has first been entered. The information is displayed on the radio's display upon the pressing of a "recall" switch. Further, if the radio is ripped out of the car, the invention can lock the information on the display. This invention shares two similarities with the system below. First, the information can only be changed by the owner. Second, it is impractical for a thief to remove the information. Bochmann's circuit improves on the idea of a serial number. It can therefore deter theft.
It is however different from the system disclosed below. First, it does not prevent theft by indicating that an item is stolen. It is possible that it can do this by displaying the rightful owner of an item. Still, this information does not by itself imply that an item is stolen. The item might just be in the hands of a friend of the owner. Second, the information can be removed from the display with the press of a button. Therefore, a thief is not forced to leave the information showing. In the case where the information is locked onto the display because the radio has been removed from its source of power, this invention can more rightly be considered an alarm with a physical deterrence feature rather than a passive system which is not tripped and which does not affect the functioning of the item it is on. Third, this invention is limited to electronic items which have memory, input and display elements. People who see the invention above probably will not know whether the item it is part of is stolen and even if they do suspect it is stolen, few will be prompted to take action. People who see the system below will know whether the item it is part of is probably stolen and many will be prompted to take action.